1. Field of Invention
The present invention relates generally to shielding reticles in lithographic systems. More particularly, the present invention relates to a blind which may be opened and closed as needed to control the projection of a laser beam through a reticle.
2. Description of the Related Art
For photolithography procedures which are used in the fabrication of semiconductors, the ability to control the procedures is important to ensure that semiconductors are accurately formed. By way of example, exposure processes which allow for the transfer of a circuit pattern from a reticle onto a wafer must be carefully controlled to ensure that the circuit pattern is accurately transferred onto a desired portion of the wafer. When the circuit pattern is not accurately transferred onto a desired portion of the wafer, the quality and the performance of semiconductors formed from the wafer may be compromised.
A laser beam generally passes through a reticle to transfer a circuit pattern from the reticle onto a wafer. To prevent the laser beam from passing through the reticle until after an appropriate area of the wafer is positioned under the reticle, reticle blinds are often used to shield the reticle from a laser until the wafer is properly positioned. Reticle blinds, which are typically used in a horizontal orientation, often utilize lead screws on mechanical bearings to enable the blinds to be opened and closed. In many applications, the reticle blinds are not capable of being opened and closed relatively quickly. When a reticle blind may not be closed relatively quickly, a reticle may remain exposed to a laser longer than desired. As a result, an exposure process may be compromised.
Some reticle blinds are arranged to be operated at higher speeds. However, when such reticle blinds are moved at relatively high speeds, disturbances and high reaction forces typically arise. Disturbances and high reaction forces often compromise the integrity of an exposure process.
Therefore, what is desired is a method and an apparatus which allows a reticle to be efficiently shielded from a laser until it is appropriate for the pattern on the reticle to be projected onto the surface of a wafer. That is, what is needed is a reticle blind which is capable of being opened and closed at a relatively high speed.